Field of the Invention
The present disclosure relates to mobile communications.
Related Art
3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) that is an advancement of UMTS (Universal Mobile Telecommunication System) is being introduced with 3GPP release 8. In 3GPP LTE, OFDMA (orthogonal frequency division multiple access) is used for downlink, and SC-FDMA (single carrier-frequency division multiple access) is used for uplink. Multiple Input Multiple Output (MIO) having up to four antennas is employed. Recently, 3GPP LTE-Advanced (LTE-Advanced) which has evolved from 3GPP LTE is widely used.
FIG. 1 Shows the Configuration of an Evolved Mobile Communication Network.
As illustrated, an evolved UMTS terrestrial radio access network (E-UTRAN) is connected to an evolved packet core (EPC).
The E-UTRAN includes a base station (BS) (or eNodeB) 20 which provides a control plane and a user plane to a User Equipment (UE). The BSs (or eNodeBs) 20 may be interconnected by means of an X2 interface.
Layers of a radio interface protocol between the UE and the BS (or eNodeB) 20 can be classified into a first layer (L1), a second layer (L2), and a third layer (L3) based on the lower three layers of the Open System interconnection (OSI) model that is well-known in the communication system. Among them, a physical (PHY) layer belonging to the first layer provides an information transfer service by using a physical channel, and a radio resource control (RRC) layer belonging to the third layer serves to control a radio resource between the UE and the network. For this, the RRC layer exchanges an RRC message between the UE and the BS.
Meanwhile, the EPC may include various constitutional elements. Among them, a mobility management entity (MME) 51, a serving gateway (S-GW) 52, a packet data network gateway (PDN GW) 53, and a home subscriber server (HSS) 54 are illustrated in FIG. 1.
The BS (or eNodeB) 20 is connected to the MME 51 of the EPC through an S1 interface, and is connected to the S-GW 52 through S1-U.
The S-GW 52 is an element that operates at a boundary point between a Radio Access Network (RAN) and a core network and has a function of maintaining a data path between an eNodeB 22 and the PDN GW 53. Furthermore, if a terminal (or User Equipment (UE) moves in a region in which service is provided by the eNodeB 22, the S-GW 52 plays a role of a local mobility anchor point. That is, for mobility within an E-UTRAN (i.e., a Universal Mobile Telecommunications System (Evolved-UMTS) Terrestrial Radio Access Network defined after 3GPP release-8), packets can be routed through the S-GW 52. Furthermore, the S-GW 52 may play a role of an anchor point for mobility with another 3GPP network (i.e., a RAN defined prior to 3GPP release-8, for example, a UTRAN or Global System for Mobile communication (GSM) (GERAN)/Enhanced Data rates for Global Evolution (EDGE) Radio Access Network).
The PDN GW (or P-GW) 53 corresponds to the termination point of a data interface toward a packet data network. The PDN GW 53 can support policy enforcement features, packet filtering, charging support, etc. Furthermore, the PDN GW (or P-GW) 53 can play a role of an anchor point for mobility management with a 3GPP network and a non-3GPP network (e.g., an unreliable network, such as an Interworking Wireless Local Area Network (I-WLAN), a Code Division Multiple Access (CDMA) network, or a reliable network, such as WiMax).
In the network configuration of FIG. 1, the S-GW 52 and the PDN GW 53 have been illustrated as being separate gateways, but the two gateways may be implemented in accordance with a single gateway configuration option.
The MME 51 is an element for performing the access of a terminal to a network connection and signaling and control functions for supporting the allocation, tracking, paging, roaming, handover, etc. of network resources. The MME 51 controls control plane functions related to subscribers and session management. The MME 51 manages numerous eNodeBs 22 and performs conventional signaling for selecting a gateway for handover to another 2G/3G networks. Furthermore, the MME 51 performs functions, such as security procedures, terminal-to-network session handling, and idle terminal location management.
Meanwhile, high-speed data traffic is dramatically increasing. In order to deal with the increasing traffic, technologies for offloading traffic from UE to a Wireless Local Area Network (WLAN) (or Wi-Fi) or a small cell have been introduced.
FIG. 2 Shows the Configuration of a Small Cell and an Additional Network which are Used to Deal with an Increase in Data Traffic of UE.
With reference to FIG. 2, a plurality of WLAN Access Point (AP)s may be arranged in the coverage of a small cell BS 31. That is, various Radio Access Technologies (RATs) may exist around an UE. Accordingly, the UE is capable of distribute data traffic to the various RATs. The small cell BS 31 may be arranged in the coverage of a macro BS, such as an existing eNodeB.
As illustrated in FIG. 2, the P-GW 53 and the HSS 54 are connected to an access authentication authorization (AAA) server 56. The ePDG 57 acts as a security node for a unreliable non-3GPP network (for example, WLAN, WiFi, or the like). The ePDG 57 may be connected to a WLAN access gateway (WAG) 58. The WAG 58 may act as a P-GW in a Wi-Fi system.
However, if a WLAN AP is added, an EPC may have a very complicated structure.
Alternatively, a user may want to use resources in his/her home network (for example, at work or at home), regardless of which WLAN AP is an accessed AP. Such a user need may be satisfied through Mobile-IPv6.
FIG. 3 Shows an Example of Bypassing a Home Network Through Mobile-IPV6.
As noted with reference with FIG. 3, a mobile IP terminal may be generated between a home agent (HA) and a remote agent (RA) in order to enable a UE 10 to access resources within a home network or to access an external network even though the UE 10 out of the home network is on a visited network 1 or on a visited network 2. FIG. 3 illustrates a case where each agent is included in a WLAN AP in each network, but aspects of the present disclosure are not limited thereto, so each agent may exist independently.
Suppose that a subnet of the home network is 10.1.1.0, that a subnet of the visited network 1 is 20.1.1.0, and that a subnet of the visited network 2 is 30.1.1.0, it is possible to use an IP address of the home network (for example, 10.1.1.1), regardless of where the UE 10 is located. To this end, The UE 10 may transmit a control message, e.g., a registration message, to a home agent (HA) to notify a location of the UE 10. Then, a mobile IP tunnel may be generated between the HA and the RA, and care of address (COA) may be performed through the mobile IP tunnel.
However, this technique may lead to a prolonged delay.
FIG. 4 shows a case in which UE#A existing in an external network (EN) transmits data to UE#B. Here, UE#B receives the data by using the cellular-based RAT and the WLAN-based RAT.
In a case where UE#B receives the data with the cellular-based RAT, an end-to-end delay between UE#B may be defined as below:E2E Delay=PDEN+PDHN+PDBN_A 
Here, PDEN denotes a packet delay in an external network, PDHN denotes a packet delay in a home network, and PDBN_A denotes a packet delay in backbone A.
In a case where UE#B receives the data by using the WLAN-based RAT, an end-to-end delay between UE#A and UE#B may be defined as below:E2E Delay=PDEN+PDVN+PDBN_A+PDBN_B 
Here, PDVN denotes a packet delay in a visited network, and PDBN_B denotes a packet delay in backbone B.
As noted with the above equation, if UE#B receives the data by using the WLAN-based RAT which is the visited network, a further delay of PDBN_B occurs.
To solve the delay problem, existing optimization schemes may be used. The existing optimization schemes may be summarized as in the following table:
TABLE 1Type of SchemeCharacteristicsDrawbacksClient ControlledA HA transmitsComplexity inOverheadMIPv6 = M *Mobility Protocolbiding information onembodiment of aC * NCN * (OAN +(MIPv6)a home address and aterminal, and increaseOBN)remote address of ain power consumptionreceiver UE (UE#B inIncrease in L3FIG. 4) to asignaling overheadstransmitter UEfor updating binding(UE#A in FIG. 4)relative to CN due tomovement of aterminalNetworkA HA transmitsBeing requested by aOverheadPMIPv6 =Controlledbiding information onspecial-purpose relayM * C * NRA * OBNMobility Protocola home address and aagent(PMIPv6)remote address of aAn increase of L3UE to a relay agent (asignaling overheadsgateway)for updating bidingbetween relay agentsdue to movement of aterminalIntegrated Web cacheStore, in a relayA need of a special-purpose gateway whichserver, contentshas an additional web cash functionfrequently searchedIn response to a request for non-cashedby userscontents, a transmission delay still occurs
In the above table, M denotes the number of times of movement, and C is 2, which is the number of transmission and receipt of binding information. NN denotes the number of devices in which connection for data communications is set, and NPA denotes the number of relay agents.
In addition, OAN denotes a sum of overheads in access networks of UE, and OBN denotes a sum of overheads in backbone networks.
As noted with reference to the above table, the existing optimization techniques are advantageous in reducing a delay, but possibly cause an increase in overheads. Thus, there is a need for a scheme which enables reducing a delay without an additional overhead.
An embodiment of the present specification aims to provide a solution of a complex structure of an evolved packet core (EPC), which is led by addition of an Wireless Local Area Network (WLAN).
In addition, another embodiment of the present specification aims to provide a solution for reducing a delay without an additional overhead.